Kyiv mayor Vitali Klitschko reported explosions in the capital about an hour after the region's military administration said unmanned aerial vehicles (UAVs) or drones had been detected in the city's airspace.

"UAV debris is burning in an open area in Desnyansky district," he said, adding that emergency services were on site.

There were air alerts in the Kyiv, Chernigiv, Cherkasy, Mykolayiv, Kherson regions as of 3:30 am (0130 GMT).

Mykolayiv's mayor said the air force had downed drones in the city, with debris causing a fire.

Also early Tuesday, Ukraine's air force reported that nine Russian Tupolev Tu-95MS strategic bombers had taken off from a far northern base.

"Preliminarily, 9 Tu-95MS strategic bombers from the "Olenya" airfield (Murmansk region) are flying in the southeast direction," the air force said.

The air force had also reported the take off of Tupolev Tu-95s, which date back to the Soviet era, on December 29.

On that day, Russia launched a wave of strikes across Ukrainian cities, including the capital, which killed 39 people.

Tuesday's drone attacks come a day after Russian President Vladimir Putin said that his forces would intensify strikes on military targets in Ukraine, after an unprecedented Ukrainian attack over the weekend on the Russian city of Belgorod.

That attack, on Saturday, killed 25 people including five children.

Moscow also hit Ukrainian cities on New Year's Eve, with Kyiv saying it had foiled a "record" number of drones launched by Russia.